Preheat your oven to 375°F (190°C). Cut the zucchini in half lengthwise. Scoop out the flesh, leaving about 1/4-inch border around the edges. Reserve the scooped-out flesh in a bowl.
Place the hollowed zucchini halves on a baking sheet lined with parchment paper. In a large mixing bowl, combine the cooked quinoa, diced cherry tomatoes, red and yellow bell peppers, red onion, minced garlic, feta cheese, chopped basil, chopped parsley, and the reserved zucchini flesh.
Mix everything together until well combined. Season the mixture with salt and pepper to taste. Drizzle olive oil over the mixture and toss to coat evenly. Stuff each zucchini half with the quinoa mixture, pressing it down gently.
If desired, sprinkle grated Parmesan cheese over the stuffed zucchini halves for an extra cheesy topping. Bake in the preheated oven for about 25-30 minutes or until the zucchini is tender.
Remove from the oven and let it cool for a few minutes before serving. Garnish with additional fresh herbs or a drizzle of olive oil if desired.